The mineral deposits of Ag-Pb-Zn quartz veins of the Santa Bárbara mining district are hosted in sedimentary rocks of the Cretaceous formed by carbonaceous shales and calcareous siltstones and minor lenses of limestone of the Parral Formation. The hydrothermal solutions, possibly emanating from an intrusive body suspected to be at depth, were introduced in into the fracture systems (Scott, 1958). According to the mineralogy of the veins, which includes sphalerite, galena, chalcopyrite, pyrite, and arsenopyrite, the deposit is considered as hypothermal formed at high temperature according to Lindgren’s classification.

The pre-mineral rock types found at Santa Barbara consist of a thick calcareous shale formation and andesite flows. The postmineral rock types consist of dikes and sills of rhyolite and diabase, a thin conglomerate formation, basalt flows, and unconsolidated stream sediments. Pre-mineral faulting took place in two stages, forming four fault systems. All faults within each system have similar strike and dip. Movement along these faults, vertical in the first-stage faults and horizontal in the second stage faults, formed openings and breccia zones.

Hydrothermal solutions, emanating from depth, were introduced into the faults. The walls and breccia fragments within the faults were silicified, and the high-temperature silicates, garnet, pyroxene, and epidote were formed. Accompanying and following the formation of the silicates, the sulfides, such as sphalerite, galena, chalcopyrite, pyrite, and arsenopyrite, with associated gold and a silver mineral, were introduced with quartz, calcite, and fluorite. Most of these minerals replaced the silicates and altered shale. The parts of the faults where wide pre-mineral openings were located filled with quartz and a higher ratio of sulfides than in the narrow portions of the faults. Quartz, calcite, fluorite, and barite were among the last minerals deposited.

The lead, zinc, copper, silver, and gold mineralization present at Santa Bárbara is associated to quartz veins and fault veins hosted by sedimentary rocks of the Parral Formation (Cretaceous). Three vein systems are currently in exploitation:
• Segovedad;
• Tecolotes;
• San Diego.

IMMSA has identified ore-shoots of up to several hundred meters in length and of more than 500 m in vertical extension, which are found in structural zones in the three vein systems. Vein width varies from less than a meter up to 20 m.

Pb-Zn-Ag quartz veins are localized along small displacement faults that cut obliquely across the
hinge zone of a broad asymmetric anticline. Single veins are more or less continuous for distances up to 800 m. Veins average about 1.5 m wide but locally may pinch and swell from several centimeters to as much as 3 m in width. Pb-Zn-Ag mineralization is found over a vertical extent of more than 500 m.

The mineralization was emplaced in several distinct vein stages that display cross-cutting relationships. Stage 1 ores contain massive sulfides: sphalerite, galena, and very minor chalcopyrite. Stage 2 ores contain abundant calc-silicates, chalcopyrite, and a small amount of gold, but only minor sphalerite and galena. Silver was deposited during both stages, but the bulk of the silver was associated with galena and deposited in Stage 1. Stages 3 and 4 contain quartz, calcite, and fluorite and are not important ore-bearing stages.

Santa Barbara includes three main underground mines (San Diego, Segovedad and Tecolotes). The mining operations at Santa Barbara are more diverse and complex than any of the other mines in Companys Mexican operations, with veins that aggregate approximately 21 kilometers in length.

Due to the variable characteristics of the ore bodies, four types of mining methods are used: shrinkage stoping, long-hole drilled open stoping, cut-and-fill stoping and horizontal bench stoping.

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The ore, once crushed, is processed in the flotation plant to produce concentrates. The lead concentrate produced is treated at a third party refinery in Mexico. The copper concentrates are treated at our La Caridad smelter and the zinc concentrates are either treated at the San Luis Potosi zinc refinery or exported.